Claw morphology, claw strength, and fighting behavior in the New River crayfish Cambarus chasmodactylus James, 1966 (Decapoda: Astacoidea: Cambaridae)

Abstract

Despite the diversity in the size, performance, and function of crustacean claws (chelae), our understanding of the functional morphology and evolution of these claws are lacking. Since crayfish claws are multi-function organs that face selection from fighting, mating, foraging, and predation, these pressures all interact to shape the claws morphology and performance. I studied a unique claw morphology, the exaggerated claw gape of the New River crayfish, Cambarus chasmodactylusJames, 1966, by investigating how this claw morphology relates to claw strength and fighting style. Claw length increased in both males and females as body size increased, although this trend was more pronounced in males, and maximal claw strength increased as claw length increased in both males and females. I describe the fighting behavior of the species in relation to previously studied species and speculate on how changes in claw morphology have led to changes in species-specific fighting style. Observations of fighting behavior in C. chasmodactylus revealed a previously undescribed claw grasping behavior, in which competitors grasp onto the manus of their opponent's claw and laterally twist to flip their opponent. When assessing the relative role of claw size and claw strength on contest success in male individuals, individuals with larger, but not necessarily stronger claws were most likely to attain dominance. These results highlight the functional morphology of a unique claw morphology and provides initial evidence for how claw form relates to fighting style within decapod crustaceans.